I was reading through one of my Road & Track mags and thought all of you might enjoy this
. I found it also online at:
http://www.roadandtrack.com/article....&page_number=1
but, i've posted it below for convenience...
For enthusiasts, the gasoline that we put into our cars' fuel tanks is liquid entertainment. We enjoy driving and like to do it enthusiastically. But there's no reason we need be profligate with fuel. That is, there are plenty of things we can do to enhance fuel economy without diminishing the enthusiast value of our motoring.
Some of these are just plain common sense. Others are more subtle, but useful nonetheless. Some can be practiced all of the time; others are for when you're feeling especially fuel-frugal or just for the challenge of it all. Specialists at Ford, Honda and Toyota contributed many of these ideas; AAA also provided useful information. Along the way, I also learned what the EPA has in mind for fine-tuning its City/Hwy Mpg ratings.
The Obvious Stuff
Good vehicle maintenance is a given. Correct tire pressures, for instance, are crucial. According to Pirelli, a 3-psi deficit translates into a 2-percent hit in economy and 5 to 10 percent more tire wear as well. Modern radials are much better in this regard than bias-ply tires of old. Nevertheless, properly inflated tires are a win-win. They enhance handling
and fuel economy.
A couple of words on mega-oversize fitments, though: Width detracts from vehicle aerodynamics, and it's not impossible that a styling statement can degrade handling, not enhance it.
What about tires with low rolling resistance? Are they worth a swap? In a word, no, especially for us enthusiasts. Generally, there's a trade of rolling resistance and ride/handling, and for once these latter two are on the same side of the equation.
Super-low-rolling resistance tires don't ride very well; nor do they grip very well. What's more (and a bit surprising), they don't wear all that well either.
The proposed EPA City and Highway values would show effect of three more evaluations, at more extreme cold, heat and speed/load. Note, for example, todays 37 City mpg would correspond to a proposed 31. City relationship is actually non-linear, slightly concave downward. Graphic by Tim Barker
As a telling point, Toyota originally fitted special low-rolling-resistance rubber to its early Prius hybrids. From 2004, though, largely in response to consumer feedback, the Prius rides on the same tires as its Corolla sibling.
One of my sources suggested that a rolling-resistance rating could be added to the Uniform Tire Quality Grading embossed on a tire's sidewall. Let consumers decide the inevitable tradeoffs among rolling resistance and the currently identified treadwear, traction and temperature. Maybe, he observes, there'd be a 2-percent reduction in fuel consumption with optimized rolling resistance. But remember you're likely to trade away grip, ride and wear.
On another matter entirely, you'd think you should take those golf clubs out of the trunk unless your trip is truly links-related. Actually, though, I learned that weight has a surprisingly minor effect. Add 100 lb. to a 3000-lb. package, and this 3-percent increase in load invokes at most a 1.5-percent penalty at the fuel pump. Of course, it's more pronounced in accelerating and braking in city traffic, least so in highway cruise.
By contrast, especially at road speeds, the effects of vehicle aerodynamics can be profound. Ski racks are particularly bad in that they're double hits: They screw up a car's CD
and increase its frontal area. (Total drag, you'll recall, is CD x A.) Original-equipment luggage racks are somewhat sleeker, until, of course, you use them to carry something.
Aero vs. A/C
The importance of aero has given rise to a good folk legend: You're better off, so goes the myth, running with your car's air conditioning on and the windows up, rather than invoking the added drag of what we used to call "440 a/c" (that is, 4 windows down, 40 mph).
The tradeoff is car- and velocity-sensitive, but my sources tell me that it's generally not beneficial at anything resembling legal speeds. Air conditioning can be as much as a 20-percent hit in fuel consumption. Unless heat and humidity call for it, you're better leaving the a/c off and the windows rolled down. (Purely as an aside, do young people wonder why we "roll down" a window?)
There's a corollary to all this concerning a climate control's Defrost setting. This mode typically activates the a/c as a dehumidifier and is certainly essential in clearing the windshield and side windows. Once they're clear, though, you're better off switching the system from Defrost to Heat; otherwise you may be running the a/c all winter long.
Revs Aren't Free &Mdash; and, Alas, Neither Is Speed
It's only in racing and with exceptions even there that "revs are free." In fact, entertaining though they may be and sonorous though they may sound revs pay a penalty in fuel consumption
and in wear.
Also, among the things under your control, one with a most profound effect on fuel consumption is your car's speed. Power requirements grow with the square of vehicle velocity (e.g., double the speed, quadruple the required power). And, obviously, power demanded is directly related to fuel consumed.
Whatever is an enthusiast to do?
When I'm canyon running, corner strafing or, just for the fun of it, beating that fellow next to me across the intersection, I think of my earlier comment about "liquid entertainment." And certainly we have the least expensive gasoline anywhere I'd want to live.
On the other hand, a lot of my motoring is rather more mundane. And there's genuine satisfaction in performing it efficiently.
WOT/Short-Shifting
Remember Coach Grimbly's dictum about "driving with an egg under your foot"? Forget it. The most efficient way to reach cruising speed is wide-open-throttle (WOT) short-shifting. That is, not only do revs cost money, but so does prolonged motoring in lower gears, when throttling and pumping losses are their greatest.
WOT/short-shifting can save as much as 20 percent in city driving, worst to best case. In actual practice, rarely does traffic allow full WOT, but it's certainly fun and efficient as well to accelerate briskly through the lower gears to whatever the ambient speed happens to be.
Once there, the appropriate choice of gear is the one that offers modest rpm with relatively large (and constant!) throttle. Here, Coach Grimbly is vindicated. Dithering the accelerator is a pure waste of fuel, as is a slice-and-dice driving style. Read the traffic and go with the flow. Said one of my sources, "In fuel-economical mode, never request more power than is necessary to get to the next deceleration." There's a good enthusiast message here: Once up to speed, maintain it.
And, of course, avoid last-instant braking that wastes both fuel and brake hardware. A word on hybrid braking: It's useful to "shape the stop," that is, not to overwhelm the instantaneous capacity of regenerative braking. What's optimal is a relatively gentle initial pedal, followed by increased pressure as speed diminishes. Some hybrids have regen gauges that help in perfecting this technique.
Last, a lot of this is manual-shift-oriented, but thoughtful mimicking with an automatic can yield benefits as well.
What About My Own Auto-Stop?
Hybrids gain part of their efficiency in automatically shutting down the gasoline engine when stopped for more than a moment. Evidently I can mimic this with my conventional car, but is it worth it?
Unless the stop is prolonged (a railway crossing, for instance), the answer is no. A conventional starter cranks its engine at 70100 rpm. Fuel and ignition are full-go, calibrated to urge the engine into action. Inherently it's a high-wear mode and not a particularly fuel-efficient one.
By contrast, hybrids have extraordinarily high-performance starting systems. For example, the Toyota Prius's spins its engine to 1000 rpm, and only then gives spark and fuel. (Withholding the fuel has an added benefit of not washing down the cylinders' lubrication.)
What about coasting down hills? Don't fuel-injection systems shut down under such conditions?
Some do, and some don't, based largely on emissions criteria. Cutting the fuel gives a spike of oxygen in the exhaust system. This, in turn, degrades the catalyst's NOx reduction, giving a spike in that pollutant when the engine restarts.
Some newer drive-by-wire throttle systems account for this by finessing the control. Nevertheless, apart from popping it out of gear as you approach a stop, coasting isn't worth it. Indeed, in many settings it's downright illegal. Plus, of course, hybrids should never be coasted. Out of gear, they're giving away all of their coast-down regen.
The Benefits of "Chaining Trips"
Linking errands and other driving activities together in a logical progression has come to be called "chaining." It's helpful simply because start-ups and short trips are fuel-gobblers. There's an interesting reason for this: With modern cars, the first priority in start-up is to light off the catalyst; this, to get emissions quickly under control. Ignition and fuel delivery are focused on this goal, even at the expense of frugality.
Hence if you reduce the cold starts, you reduce fuel consumption. By the way, what with engine coolant at 200 degrees Fahrenheit, even a nice ambient 80 degrees qualifies as a cold start.
I've Got This Neat Fuel-Saving Gizmo...
What of fuel gizmos? Briefly, save your money. Noted one of my sources, "The engine burns its fuel with 99-percent efficiency. The inefficiencies are heat-induced, not related to fuel burn." Said another, "Such gizmos enhance the financial transfer from your pocket to the seller's."
Automakers have tremendous incentive to improve their products. Anything with legitimate cost/benefit ratio and, thus, real advertising advantage would be accepted in an instant.
For example, driving aids, gizmos giving information that augments fuel frugality, can be of real benefit. One example is tire-pressure monitoring. Another is a hybrid's regen meter to help the driver optimize braking techniques.
EPA City/Hwy, Revisited
There's controversy concerning the Environmental Protection Agency's current City and Hwy ratings, and the EPA has proposed changes. However, the problem isn't necessarily in the testing. (See this month's "
Tech Tidbits".)
EPA estimates of fuel economy are based on laboratory tests performed under controlled conditions. This cuts both ways: They're repeatable (crucial of any good science) and thus an excellent comparator. But they're also purely reflective of these test conditions, and hence cannot hope to mimic the multitude of varied driving modes in the real world.
Briefly, each car is driven on a chassis dynamometer, a calibrated treadmill of sorts. Its exhaust emissions are captured and analyzed, a technique called carbon balance used to assess the fuel consumed. (Carbon balance, by the way, is much more accurate than any volumetric measurement.)
The City Cycle, aka FTP (Federal Test Procedure) nee LA4, is 1372 seconds in duration, a 7 1/2-mile simulation of a trip around downtown Los Angeles during the rush hour. Its average speed is 19.7 mph; its 22.9 minutes includes 18 stops and some 4 minutes of idling. The Hwy Cycle is based on a suburban/exurban jaunt around Ann Arbor, Michigan, home of a principal EPA test facility.
Two decades ago, in an effort to match consumer experience, the EPA devised correction factors for these results. Since then, the published City number has been 10 percent less than the test value; the Hwy, 22 percent less.
Son of EPA City/Hwy
This time around, again in response to complaints of mismatching the real world, the EPA has proposed other changes.
The final values would incorporate three other tests, these other evaluations already being performed, albeit for reasons of emissions, not fuel measurement.
The first is essentially a frigid version of the City cycle, with ambient temperature of 20 degrees Fahrenheit (versus the nominal 73 degrees Fahrenheit of ordinary testing).
The second is a rather more aggressive Hwy test, with top speeds beyond the current 60 mph and higher power demands.
The third is a 10-minute cycle essentially with air conditioning in full operation. Simulating a sunny day in Phoenix but with Houston humidity, it's run at 95 degrees Fahrenheit after the car has had a hot soak under a sun lamp.
Fuel-consumption results from these phases would be incorporated into the basic values and the results reported, but with a new Combined Mpg. Its proposed split would be weighted 43/57, City/Hwy, respectively, as opposed to the 55/45 currently in force.
The EPA's goal is to have these modifications in place for the 2008 model year (which begins as early as January 2, 2007). Generally, EPA City/Hwy values would be lower. However, the values wouldn't be diminished by a uniform factor. (See "
Tech Tidbits" and "
The Hybrid Payoff" for discussions of the non-linearity of mpg.) The chart at left gives some idea of the existing versus the proposed new values.
This is all very interesting, but I wouldn't bet heavy it'll improve matters. For lots of reasons we've touched on here, the real-world range of fuel consumption is simply enormous. Nor would I ignore current EPA ratings. On a car-to-car basis, they're generally an excellent comparator.
With the exception of hybrids: Auto-stop really helps a hybrid's EPA City number. (Note the "backward" order for some of them, their City being better than Hwy).
In any case, and in conclusion, a hybrid isn't the only way to save fuel. Indeed, its fuel payoff carries at best tenuous economics. ("
The Hybrid Payoff" offers analysis of this, together with plenty of reasons for enjoying these gasoline/electric variants.) Even if you're not into hybrids, though, "Your mileage may differ" and all for the better.
The Frugal Beetle
Many years ago when the original Volkswagen Beetle was quite the thing, a staff member at R&T's sister publication
Car Life bought one and began to brag about its exemplary fuel economy.
Colleagues decided to help things along. Every couple of days, they'd surreptitiously add a gallon of gasoline to the Beetle's fuel tank.
"The mileage is getting even better!" the staff member would exclaim.
Colleagues kept mum and continued the trick for some time.
"You wouldn't believe the mpg now!" he said.
Then they changed tactics: Every few days, they'd siphon a couple of gallons out of the tank.
"I don't know what's wrong," he said, "I'm not driving any differently and the car seems to be running okay..."
As they say, "Your mileage may differ."
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